Microelectromechanical systems (MEMS) are machines fabricated on a microscopic scale using surface micromachining or LIGA processes. MEMS devices can include moveable members (e.g. gears, rotors, linkages, levers, hinges and mirrors) for applications including sensing (e.g. acceleration or chemicals), switching (electrical or optical signals) and optical display (e.g. moveable mirrors) functions. MEMS devices can further include actuators or motors for driving gear trains to perform various functions including coded locks and self-assembling structures.
A particular problem in the development of MEMS devices is sensing the movement of particular members or elements within the device, for example, to determine a mechanical state of the device. In many types of MEMS devices (e.g. accelerometers), capacitive sensing using one electrode on the moveable member and another electrode on the substrate is adequate to measure movement of the members. However, in many other types of MEMS devices, capacitive sensing is difficult to implement, either due to problems of making electrical connections to the moveable members (e.g. a gear rotating on a hub), due to overlapping members (e.g. meshed gears), or due simply to a small size of the moveable members which limits the amount of capacitance and thereby presents signal-to-noise problems. As MEMS devices become increasingly complicated, the need for adequate sensing of movement becomes important.
An advantage of the apparatus and method of the present invention for optically sensing motion in a microelectromechanical system is that the light used to sense the motion of a moveable member does not perturb the motion of the member.
Another advantage of the apparatus and method of the present invention is that a direction or an extent of movement can be sensed.
A further advantage is that a particular mechanical state of a microelectromechanical system can be ascertained.
Yet another advantage of the present invention is that a performance characteristic (e.g. a uniformity of motion, a spring coefficient, a damping coefficient, torque supplied by a driving member, or friction of a driven member) of a microelectromechanical system can be determined.
Still another advantage of the present invention is that the apparatus and method can be used to collect information to assess failure mechanisms or reliability of a microelectromechanical system.
Yet a further advantage is that a feedback loop can be implemented using the apparatus and method of the present invention to measure a performance characteristic of the microelectromechanical system and to provide corrective feedback to the system, thereby improving operation and reliability therein.
These and other advantages of the method of the present invention will become evident to those skilled in the art.